Loudspeaker devices and systems, such as those situated in vehicle like cards, are commonly used for providing audio output to listeners. Electrical signals that are representative of various characteristics of sounds are transformed by a loudspeaker device into vibrating movements of a diaphragm. These movements of the diaphragm create sound waves that can be heard by listeners. A loudspeaker device typically employs a magnetic driving device causing a diaphragm elastically supported at a frame of the loudspeaker device to move back and forth. This vibration creates sounds that are produced by the loudspeaker. The frame may be enclosed by a housing of the loudspeaker device. When the loudspeaker device is a subwoofer, solutions are known in which an air communication duct connects an inner space of the housing to an outside space.
Low frequency loudspeakers are known which comprise a rear box. A loudspeaker box such as shown in FIG. 1 requires a relatively large space, typically 20 liters, for a high-performance subwoofer. The loudspeaker device 200 comprises a magnetic driving unit 230 and a frame 240 which is attached to a diaphragm 250. The loudspeaker device 200 is enclosed in a rear box 280. Space is always valuable in a vehicle, so that often current loudspeaker boxes are too small for a good performance. A well performing loudspeaker box is quite large, some being up to 50 liters in size.
U.S. Pat. No. 8,804,991 B2 discloses a loudspeaker assembly for use in a loudspeaker system having infinite baffle topology. The assembly comprises a driver including a cone and a basket and at least one Helmholtz resonator including a chamber and a vent duct communicating with the chamber and adapted to pass through the infinite baffle. The chamber is dimensioned to provide a tuned frequency well above an operating band associated with the driver. The cross-sectional area and length of the vent duct may be set to provide control over duct air noise and low frequency extension.
A speaker with baffle open at the rear, such as in FIG. 2, is typically only available in vehicles with a rear parcels shelf (sedan type body), so not all cars can have these. Such a loudspeaker device 200 also comprises a magnetic driving unit 230 and a frame 240 which is attached to a diaphragm 250. Here, the frame 240 is mounted to an acoustic baffle panel 290 having infinite baffle topology.
Another known solution is described in EP 2 941 011 A1. FIG. 3 depicts a subwoofer using a Helmholtz resonator tuned above the used bandwidth as a port to the outside of a closed space. FIG. 3 shows a known arrangement 100 of a loudspeaker device 200 which is installed at a wall of a vehicle including a vehicle panel 300 (such as a vehicle body) which has an opening 500 which is covered by a cap 400, such as made of plastic. The loudspeaker device 200 comprises a housing 210 including an air volume V10 which is communicated through an air communication duct 220 with an outside space V20 of the vehicle. The loudspeaker device 200 further comprises a magnetic driving unit 230 and a frame 240 having a radius a which is attached to a diaphragm 250.
Such an arrangement 100 enables the loudspeaker device 200 to be placed in small locations, such as in a vehicle side space adjacent to a vehicle panel. For providing the air communication duct 220, an opening 500 needs to be provided in the vehicle panel 300, which may be forming part of the vehicle body. Typically, such an opening 500 is a dedicated hole in a vehicle structure, such as a vehicle panel. Such a subwoofer is smaller, but needs a duct 220 through a vehicle partition panel separating an inside space from an outside space and an enclosure geometry for creating volume V10 to form a Helmholtz resonator. This may be difficult to implement regarding mechanical design.
FIG. 4 shows another known arrangement 100 of a loudspeaker device 200 which is installed at a wall of a vehicle including a vehicle partition panel 300 (such as a vehicle body) which has an opening 500, e.g. of circular shape. The loudspeaker device 200 comprises a frame 201, a diaphragm 202 elastically supported at the frame 201, and a magnetic driving device 203 including a voice coil 203a that provides driving power for operating the diaphragm 202. The frame 201 may be connected by a supporting bracket 204 to a chamber case 205 enclosing an air chamber 206 between the chamber case 205 and the diaphragm 202. A duct member forming an air communication duct 501, e.g. of circular shape, is connected to the chamber case 205 at a central opening thereof.
Accordingly, with vibration of the diaphragm 202, an air volume of air chamber 206 is communicated through air communication duct 501 with an outside space of the vehicle on the other side of the vehicle partition panel 300 forming an outer space, whereas the side of the vehicle partition panel 300 facing the loudspeaker device 200 is delimiting an acoustic space of the vehicle. Such an arrangement 100 enables the loudspeaker device 200 to be placed in locations such as in a vehicle side space adjacent to a vehicle panel. For providing the air communication duct 501, an opening 500 needs to be provided in the vehicle panel 300.
For example, as typically employed with such loudspeaker devices, the loudspeaker device 200 has a resonance frequency such as 100 Hz. At a frequency range over the resonance frequency, the sensitivity to driving power does not change largely according to change of driving frequency, and sound quality is good. But at a range under the resonance frequency (for example 20-100 Hz), the sensitivity to driving power changes largely according to change of driving frequency, and sound quality is bad.
EP 2 654 319 A2 discloses a speaker which includes a magnetic circuit, a voice coil, and a diaphragm, which are disposed in a case. The case is placed in an engine compartment of an automobile. Reproduced sound is emitted to a cabin space through a duct protruding outward from the case. A partition wall, which is a metal body frame of the automobile, is present between the engine compartment and the cabin space. The duct is inserted into a hole formed in the partition wall so that a sound port faces and protrudes into the cabin space. A heat dissipation port is formed in the case, and an end surface the magnetic circuit adjacent to the partition wall is exposed in the heat dissipation port. An elastically deformable thermal conductive sheet is inserted into the heat dissipation port so as to be sandwiched between the partition wall and the end surface of the magnetic circuit.
As an improvement for the above described problem, EP 2 654 319 A2 achieves lowering of the resonance frequency by providing an air chamber having a duct that communicates with an opposite side space across the vehicle partition panel. The air chamber creates a non-elastic resistance (inertial resistance and frictional resistance) and the resonance frequency drops (for example to 70 Hz). Accordingly, a change rate of the sensitivity becomes small at a low frequency range (for example 70-100 Hz) and sound quality at the range improves. However, on the other hand, space consumption increases significantly by providing such an air chamber having a duct in a vehicle.